According to the model recently proposed staphylococcal penicillinase induction proceeds by the following mechanism; growth of cells in the presence of inducer (e.g., penicillin) causes the newly synthesized antirepressor molecules, which seem to be formed constitutively, to acquire an active conformation. This conformation prompts the antirepressor to interact with, and thereby inactivate, the penicillinase repressor. Inactivation of the penicillinase repressor permits transcription of the penicillinase structural gene, and, subsequently penicillinase synthesis occurs. We are currently examining the correctness of this model by physico-chemical means.